The present invention relates to low-pressure electronic devices for the production of high-intensity electron and ion beams. It has particular application to supported-gas-discharge sputtering devices, devices requiring high-intensity ion beams for simultaneous evaporation and sputter deposition, and high-intensity electron beams for melting, casting, evaporating or welding, as well as other applications requiring such high-intensity ion or electron beams. For purposes of this application the term "supported-gas-discharge sputtering device" is intended to include sputtering devices having a heated cathode capable of producing thermionic emissions.
Enhanced electron emissions have previously been obtained through use of thin films of easily polarized materials on cathode surfaces. Various films and dispensing mechanisms are described in Kohl, "Cathodes and Heaters," Handbook of Materials and Techniques for Vacuum Devices (Reinhold Publishing Corp., New York 1967, pages 484-503). The films are an admixture of the base material such as tungsten and an additive of an electropositive nature that is easily polarized. Additives of low-work-function materials such as cesium, cerium, barium, thorium, lanthanum, uranium, yttrium and zirconium are suggested for production of thin films that will exhibit thermionic work functions of lower magnitude than that of either the additive or the base metal. However, the use of such thin-film emitters has been limited due to additive loss from evaporation and sputtering during operation of the vacuum device. Various means of replenishing the additive at the cathode surface have been suggested, but none have proven completely satisfactory. For example, replenishment from the vapor phase is generally impractical in high-vacuum devices. In other systems, the additive is dispensed from the interior of the cathode, but its diffusion into the surface film may not be sufficient to offset loss.